[gst-devel] add latency to audio in gstrtpbin

[Wim Taymans]

On Thu, 2008-09-04 at 11:34 -0400, Tristan Matthews wrote:
> Thanks for the feedback Eric. I had seen the RFC before but that book 
> looks pretty useful as well.
> My concern isn't that the AV will get out of sync in 
> gstreamer/gstrtpbin, but rather that it will be out of sync immediately 
> at the capture stage, i.e. if i have video input from a camera with more 
> latency than a separate audio source. An example scenario is given here:
> http://chris.pirillo.com/2007/07/11/audio-video-capture/
> where you have video of someone clapping and you have to adjust the 
> delay to make the sound and image of the clap line up.
> I would need to be able to manually adjust the latency to ensure the 
> video and audio are sync'd. Should I just put the audio through a 
> Ladspa-delay or is their a better solution in gstreamer?
> 

This situation can not occur in gstreamer when you have a well written
source element that generates correct timestamps and reports its latency
correctly. You could write an element that applies an offset to all
timestamps on the buffers.

Wim


> -T
> 
> Eric Zhang wrote:
> > Hi, Tristan:
> >
> >     You should not adjust video/audio latency manually because RTP 
> > provides a mechanism to accomplish this, called `lip-synchronization'. 
> > Refer to RFC 3550 or book `RTP: Video and Audio for the Internet' for 
> > more details. These will help you a lot.
> >
> > Eric Zhang
> >
> > 2008/9/3 Tristan Matthews <tristan at sat.qc.ca <mailto:tristan at sat.qc.ca>>
> >
> >     Hi,
> >
> >     If I have a pipeline using gstrtpbin (similar to the example in the
> >     documentation) to send audio and video, what is the best/most reliable
> >     way of adding latency to the audio? Would gst_event_new_latency work
> >     (and if so, how), or am I missing its intent:
> >     http://gstreamer.freedesktop.org/data/doc/gstreamer/stable/gstreamer/html/gstreamer-GstEvent.html#gst-event-new-latency
> >
> >     Basically my concern is that if video capture is too slow, can I
> >     manually adjust the audio latency to match.
> >
> >     Best,
> >
> >     Tristan
> >
> >     --
> >     Tristan Matthews
> >     Société des arts technologiques [SAT]
> >     email: tristan at sat.qc.ca <mailto:tristan at sat.qc.ca>
> >     web: http://www.music.mcgill.ca/~tmatthews
> >     <http://www.music.mcgill.ca/%7Etmatthews>
> >
> >
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